When microorganisms, cells or tissues of animals or plants, or the like are cultured, it is extremely important for culture control to measure the concentrations of hydrogen ions, sodium ions, other monovalent cations, and the like in culture liquids. In general, combination electrodes for ion concentration measurement (hereinafter, simply referred to as “combination electrodes” in some cases) are used for this measurement.
A combination electrode for hydrogen ion concentration measurement, which is a so-called pH combination electrode, is known as a typical example of the combination electrodes for ion concentration measurement. FIG. 4 schematically shows an example of the structure of the combination electrode.
In the figure, the combination electrode 51 for ion concentration measurement includes a glass electrode (ion-selective electrode) 52 and a reference electrode 53.
The glass electrode 52 has a glass support tube 54 whose upper end is sealed, and which has a sensitive glass membrane 55 at a lower end thereof.
Here, an electric potential generated on a surface of the sensitive glass membrane 55 is generally taken out of the glass support tube 54 by a glass electrode internal solution 52a (a phthalate buffer solution or the like) housed on an backside (inside) of the sensitive glass membrane 55, and by: a silver wire of silver-silver chloride serving as a glass electrode internal electrode 52b; or a platinum wire 52c which is connected to an end portion of the silver wire in the glass support tube 54, and which penetrates an upper end-sealing portion. Then, the electric potential is transmitted to a lead wire (not illustrated) to a potentiometer through a terminal 60x for a glass electrode of a terminal portion 60, which will be described later.
Note that the silver wire of the internal electrode 52b may be employed for the portion penetrating the upper end-sealing portion of the glass supporting tube 54. Alternatively, a platinum wire, which has a thermal expansion coefficient close to that of glass, is often employed for the portion in a way that the platinum wire is sealed with glass.
The reference electrode 53 includes a closed reference electrode chamber 58 whose upper and lower surfaces are sealed, and which houses a reference electrode internal electrode 53b made of silver-silver chloride and a reference electrode internal solution 53a (a potassium chloride solution or the like). The reference electrode chamber 58 is formed inside an outer tube 57 and around the glass support tube 54. The outer tube 57 is made of glass or a synthetic resin, and has a liquid junction 56 near a lower end thereof. The glass support tube 54 is placed penetrating the outer tube 57 along a substantially center axis of the outer tube 57.
Note that the reference electrode internal solution 53a contains 1 to 5% (W/V) of a thickener (for example, carboxymethyl cellulose (CMC) or the like) in some cases, to prevent excessive seepage of the reference electrode internal solution 53a through the liquid junction 56 due to thermal expansion of the reference electrode internal solution 53a during a sterilization treatment of the combination electrode 51, which will be described later.
For the sealing of the upper surface (annular) of the reference electrode chamber 58, a filler of a synthetic resin (for example, a silicone resin or the like) being filled in an annular shape for sealing is used generally as a sealing means 59. Meanwhile, the sealing of the lower surface of the reference electrode chamber 58 is achieved, for example, by being melted and integrally welded to a portion near a lower end of the glass support tube 54, as shown in the figure, or by using a gasket.
Here, an electric potential of the reference electrode internal electrode 53b is taken out of the reference electrode chamber 58 by a silver wire of the reference electrode internal electrode 53b penetrating the sealing means 59 in the vertical direction. Then, the electric potential is transmitted to a lead wire (not illustrated) to a potentiometer through a terminal 60y for a reference electrode of the terminal portion 60, which will be described next.
The terminal portion 60 provided above the glass electrode 52 and the reference electrode 53 is configured such that the rod-shaped terminal 60x for a glass electrode is installed upright, while penetrating a sealing member 60z (for example, a filler of a synthetic resin (Example: polytetrafluoroethylene) or the like) along a substantially center axis thereof. The sealing member 60z sections the inside of the cylindrical terminal 60y for a reference electrode in the vertical direction.
In addition, the terminal portion 60 is connected to the glass electrode 52 and the reference electrode 53 by inserting and fixing the terminal portion 60 and an upper portion of the outer tube 57 into and to a cylindrical connecting member 61 in the vertical direction.
Note that an outer periphery of the terminal 60y and an inner periphery of the connecting member 61 are liquid-tightly fixed to each other by an adhesive agent made of a synthetic resin.
In addition, the impedance of the sensitive glass membrane 55 is generally as high as around 100 MΩ. Hence, an insulating property far greater than the impedance is required between the terminal 60x and the terminal 60y. Accordingly, the sealing member 60z needs to have an insulating property, and to avoid deterioration in insulation due to attachment of water or the like.
In a portion (a space portion and the like) 62 formed by being surrounded by a lower surface of the sealing member 60z of the terminal portion 60, an upper surface of the sealing means 59 of the reference electrode chamber 58, the glass support tube 54 and the like, and an inner peripheral surface of the connecting member 61, an end portion of the platinum wire 52c (or a silver wire, hereinafter the same shall apply) led to the outside of the glass support tube 54 and an end portion of the silver wire led from the reference electrode internal electrode 53b to the outside of the reference electrode chamber 58 are connected to lower ends of the terminal 60x and the terminal 60y, respectively. Here, the space portion and the like 62 is left as a space portion, as it is, or is filled with a filler of a synthetic resin (for example, a silicone resin or the like), for example.
In addition, a male screw 61a is provided on an upper outer periphery of the connecting member 61. A connector (not illustrated) to be connected to a potentiometer through a lead wire is screwed to the male screw 61a. Thereby, electric potentials of the glass electrode 52 and the reference electrode 53 are transmitted to the potentiometer.
Note that reference sign 61b denotes an O-ring interposed between the inner peripheral surface of the connecting member 61 and an outer peripheral surface of the outer tube 57, and reference sign 61c denotes an O-ring for liquid-tightly mounting a sterilization cap, which will be described later (see Non Patent Literature 1).